This invention relates to systems for preventing accidental erasure of, or writing over, computer program information stored on so-called floppy diskettes (called "write protecting" or WP) and for ensuring the proper frequency of disk rotation and the proper alignment and orientation of such diskettes in disk-drive apparatus (called "diskette-positioning" or "disk-positioning" or DP). Specifically, the invention concerns write-protection and disk-positioning systems that enable use of both sides of the floppy diskette.
Over the past decade, growth and development in the mini- and microcomputer field have been extraordinary; yet in most instances, only one side of the floppy diskettes used with such computers is available to store information, due to limitations imposed by the disk drive and its interaction with the write-protect and disk-positioning systems as described below.
Floppy diskette units consist of two parts, an extremely thin, round flexible disk coated with a magnetically responsive substance and a firm square permanent jacket that houses the disk. The jacket protects the disk and provides stiffness to enable insertion of the disk/jacket unit into disk-drive equipment. As the disk is rotated rapidly within the stationary jacket, the disk-drive equipment records on and reads from one side of the disk through a jacket slot that extends over the active area of the disk.
The write-protect mechanism includes a notch in the one edge of the jacket which is sensed by the disk drive, for example by a spring-loaded pin that is blocked in the absence of the notch. Uncovering the notch allows the pin to extend through the notch and thereby trigger the write-protect function (or, in some systems, the write-enable function) on the disk drive. Covering the notch has the opposite effect.
For many, but not all, disk-drives, the system for disk positioning requires two small holes aligned on opposite sides of the disk jacket and, for soft-sector diskettes, one smaller corresponding hole in the disk, radially aligned with the jacket holes (hard-sector diskettes have multiple disk holes in a circle radially aligned with the jacket holes). A light source is positioned inside the disk drive on one side of the disk/jacket unit, and a sensor is aligned on the other side, so that, when the disk/jacket unit is correctly positioned and begins to rotate, the sensor periodically senses the light through the jacket and disk holes. If the unit is not properly positioned, it will block light from the sensor, and the disk drive will not read from or write on the disk; similarly, if the disk is not rotating at the proper frequency the disk drive will not transfer information to and from the disk.
Most disk-drive read and write devices are "single-sided"--that is, they interact with only one side of the inner disk--but both sides of the disk are coated with magnetic material, and both sides of the disk are accessible through slots in the jacket. For existing disks, correct orientation of the write-enable notch and the positioning holes will always present the same side of the disk to any given single-sided read and write apparatus.
Modification of a diskette to enable use of both sides is complicated by the fragile nature of the inner disk and the effect of pressure, abrasion, bending, foreign material, or magnetic fields on that disk. Extreme care must be used to avoid touching or bending the disk.
It is possible to make ad hoc modifications to the diskette to enable use of both sides as described in 80 Microcomputing, Oct., 1980, pp. 140-2. Specifically, that article shows a process in which holes or notches are outlined on the jacket using a traced flat pattern, and an ordinary punch is positioned by hand between the jacket and the disk to punch the marked holes. Such methods pose a significant danger of damaging the disk in that they may lead to substantial bending of the diskette, and they require inserting fingers or harmful foreign material between the disk and the jacket. Moreover, such methods are time-consuming, are not necessarily reliable, accurate or repeatable, and require a significant amount of care. Save for such methods, one side of the floppy disk has been virtually wasted for many years.